Submergible screw-type dental implant and method of utilization

ABSTRACT

A submerigible screw-type implant includes a longitudinal channel which directs bone chips towards the base of a bore in the patient&#39;s bone in which the implant is installed. These bone chips promote autogenous rapid regrowth of new bone to securely anchor the implant in place. In order to be able to position the implant at the most advantageous angle at the edentulous sight, angled abutments for supporting an artificial tooth structure or angularly adjustable abutments are provided. The angularly adjustable abutments may be in the form of a ball and socket joint in which the socket includes an inner casing having a peripheral extension that acts to lock the joint at the desired angle. Also, the support for an artificial tooth may include a shock-absorbing cushion to prevent some of the forces of mastication from disturbing the implant.

This is a continuation of application Ser. No. 025,942, filed Mar. 16,1987, now U.S. Pat. No. 4,842,518, issued June 27, 1989, which is acontinuation-in-part of Patent Application Ser. No. 904,381 filed Sept.4, 1986and now abandoned.

TECHNICAL FIELD

This invention relates to dental implants and, more particularly, tosubmergible screw-type implants

BACKGROUND ART

Screw-type implants are well known in the art. U.S. Pat. No. 3,499,222of L. I. Linkow et al. discloses screw-type implants which may be buriedin the alveolar ridge crest bone of a patient in an edentulous region.The implant has a threaded lower portion which may be screwed into anopening created in the bone after the tissue has been displaced. Acoronal portion protrudes above the bone and is used to support anartificial dental appliance, e.g. an artificial tooth or bridge.

In more recent year's submergible implants have been created in whichthe threaded portions of the implants can be completely embedded in thebone. They may then be covered with tissue and allowed to remain inplace while new bone grows around the implant and through vent holes init. Once it is firmly anchored in new bone (3 to 6 months), the tissueis reopened and an upper post portion is screwed into the implantportion and is used to mount the artificial dental device.

It is advantageous when installing an implant portion in the patent'sbone, if the implant is self-tapping in a bore created in the bone. Thiscauses it to be anchored better. Also, it would be advantageous if thebone chips created during a self-tapping operation were deposited intothe bore or opening because these chips promote faster bone growthbecause of their autogenous nature.

In order to align the artificial tooth or other dental devices with theother teeth of the patient, it may be necessary to have the post portionat an angle to the implant portion. This may be accomplished by bendingthe post portion so that its head is at an angle to the threaded shaft.This bending may be accomplished before the post is threaded into theimplant portion or afterward. If the post is bent before attachment tothe implant, the proper alignment is difficult to achieve. If bent afterattachment, there is a danger that too much stress will be put on theimplant portion and it will loosen in the bone and fail. Also bendingthe post may fatigue the metal of the post and cause breakage.

DISCLOSURE OF THE INVENTION

The present invention is directed to a dental implant which, in itspreferred form, is of the submergible screw type with a longitudinalchannel or slot through the threads so as to improve their self-tappingability. The implant also has an angled swivelable connector to allowthe post for supporting an artificial dental appliance to be positionedin proper alignment with other teeth in the patient's mouth withoutapplying stress to the implant.

In an illustrative embodiment of the invention, the implant portion ofthe device includes a threaded region that contains a longitudinalchannel through a portion of the outer parts of the threads. The channelis wider toward its bottom. One side of the channel is at a right angleto the implant circumference so as to create a cutting edge that assistsin the formation of a self-tapping capability for the implant when it isinstalled in a bore or opening in the patient's bone. The other side ofthe channel is at an oblique angle to the circumference.

The channel guides bone chips created during the threading of theimplant toward the base of the bore in the bone. By terminating thechannel below the uppermost threads, epithelial tissue is prevented fromgrowing down into the bone along the channel.

The post or abutment portion of the implant which supports an artificialdental appliance may be a straight portion on to which the appliance isthreaded. However, in situations where it must be at an angle to theimplant portion the abutment may be a separate piece from the implantportion and may be attached thereto at an angle by means of a connectionportion of the abutment. The connection portion may be in the form of arotatable beveled collar, a ball and socket joint, or other suitablemeans that allow the post to swivel about the axis of the implantportion and/or to assume various angles with respect to that axis. Oncein place, means are provided for securing the abutment against furthermovement with respect to the implant portion. As a result the implantcan assume a desired angle to assure proper alignment of the artificialdental structure with the other teeth of the patient along the occlusalplane.

In one version the abutment may include an elastic ring This ringflexibly separates an upper portion and lower portion of the abutment,much in the manner of a shock absorber. With this arrangement some ofthe shock of mastication is buffered so that it is not applied directlyto the screw implant.

The present invention also contemplates a unique surgical method. Withthis method an incision is made in the tissue covering the alveolarridge crest bone. This underlying bone is then exposed and a bore isdrilled into the bone at a depth sufficient to hold the implant portionof the device. The bore is made slightly smaller in diameter than theimplant device and is at an angle which will allow it to engage themajor portion of the available bone. Then the implant device is threadedinto the remaining bone about the bore utilizing its self-tappingthreads and the self-tapping feature of the channel along its length. Itis typically buried at a depth such that it is submerged below the uppersurface in the bone and is completely buried in the bone.

During the insertion procedure bone chips are removed from the walls ofthe bore while forming the grooves in the bone which match the threadsin the implant. These bone chips drop along the channel to the base ofthe bore and help to promote growth of new bone which firmly anchors theimplant in place.

Threading of the implant portion into place may be accomplished with ahexagonal projection or recess located at the free end of the implantportion. This hexagonal section is connected to a wrench-type device toscrew the implant into the bone.

Once secured in place a cover of minimal height may be attached to theexposed surface of the implant portion by a screw passing through thecover and threaded into an aperture in that surface. The tissue may thenbe sutured over the implant cover. New bone is allowed to grow and toanchor the cover and implant firmly in place. Several weeks or monthslater, the tissue is opened again and the cover is removed. A threadedabutment or post is then attached to the threaded aperture in the end ofthe implant portion. This abutment is used for supporting the artificialdental appliance.

The angle at which the implant portion is located in the bone may not bethe most conducive to the proper alignment of the artificial tooth orother dental devices with the remaining teeth of the patient. As aresult, the abutment includes an angled, swivelable connection portionfor attaching the abutment to the implant portion. In one embodimentfixed angular devices which are rotatable about the longitudinal axis ofthe implant are utilized, and in another embodiment the part iscontinuously swivelable to any desired angle. In either case, after theabutment or support for the artificial tooth is at the proper angle, itis locked such that it remains in that position. Finally, the tissue isclosed about the abutment an the artificial tooth or bridge support iscemented or screwed to the abutment.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other features of the present invention will be morereadily apparent from the following detailed description and drawings ofillustrative embodiments of the invention, in which:

FIG. 1 is a schematic cross section of the side of a patient's faceshowing the alveolar ridge crest with a screw type implant according tothe present invention installed therein;

FIG. 2 is an enlarged view of an illustrative embodiment of the implantportion of the device of FIG. 1 with an external hex projection;

FIG. 3 is a top view of the implant portion of FIG. 2 showing theexternal hex portion;

FIG. 4 is a cross-sectional view through the implant portion of FIG. 2along line 4--4 showing the cross-sectional shape of the channelaccording to the present invention;

FIG. 5 is an implant portion of a screw-type implant according to thepresent invention with an internal hex recess;

FIG. 6 is a illustrative embodiment of a completed screw-type implantwith an angularly positioned threaded shaft attached thereto;

FIG. 7 is a cross-sectional view of a ball and socket connection portionof an abutment according to the present invention;

FIG. 8 illustrates a modification of the ball and socket joint of FIG.7;

FIG. 9 illustrates a further modification of the ball and socket jointof FIG. 7;

FIG. 10 is a ball and socket joint connection portion with a stationaryball;

FIGS. 11A and 11B are cross-sectional views of a unitary inner casingand a two-part inner casting, respectively;

FIG. 12 is a side view of a healing collar according to the presentinvention;

FIGS. 13 and 14 are front and side sectional views of an artificialtooth with an abutment according to FIG. 7;

FIG. 15 is a cross-sectional view of an embodiment of an abutment with ashock-absorbing cushion; and

FIG. 16 is an alternative embodiment of the screw of the shock-absorbingabutment of FIG. 15.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The present invention contemplates at least a two part screw-type dentalimplant, i.e, an implant portion 10 which is buried in the bone of thepatient and a post or abutment portion 20 which is attached thereto andwhich supports an artificial tooth structure 30. As shown in FIG. 1, animplant screw portion 10 is located in a bore in the aveolar crest 11 atan angle that causes it to be in the center of the thickest portion ofgood available bone. The abutment 20 is attached both to the implantportion 10 and the artificial tooth 30, and is set so that the tooth isat an angle to the implant which causes the tooth to be in properalignment.

In FIGS. 2 and 3 the screw implant portion 10 of FIG. 2 is illustratedin more detail. This implant portion 10 contains threads 13 which extendover the middle region of the implant portion. These threads may have aflat bottom and be angled up to form a Christmas tree shape in crosssection. The lower half of the implant portion 10 contains a cavity 14(shown in dotted line). Also, spaced about the lower end of the implantare holes or vents 16, 16a and 16b, which penetrate from its exterior tothe interior cavity 14. The purpose of these vents is to allow new boneto grow through and into the center cavity in order to firmly anchor theimplant in the patient's bone. The upper surface 17 of the implantportion defines a threaded aperture 19 which is used to connect theabutment 20 to the implant portion 10. The projecting structure 12 whichforms surface 17 has a hexagonal shape as shown more clearly in FIG. 3.This hexagonal shape allows a tool, e.g. a wrench, to be used to rotatethe implant portion so as to thread it into the patient's bone.

According to the present invention a channel 18 is cut through thethreads 13 and possibly into the outer casing of the implant portion 10.As depicted in dotted line in FIG. 3 and in cross-section in FIG. 4, thechannel 18 is one of three channels 18, 18a, 18b in a typical implantportion. These channels are made to intersect the respective vents 16,16a and 16b which are spaced at angles of 120 about the circumference ofthe implant portion 10. The channels do not extend completely toward theupper surface 12 in order to prevent tissue from growing down along thechannel, and to prevent the incursion of food and bacteria. It should beparticularly noted in FIG. 4 that the channels 18 have one edge which isat about 90° to the circumference of the implant, i.e., surface 18', andanother more obliquely shaped edge, i.e. surface 18".

During installation of the implant, an incision is made in the gumtissue of the patient and the underlying bone is exposed. Then a drillor burr is used to make an opening or bore hole in the bone which isslightly larger in diameter than the implant portion body 10, but whichis not as wide as the threads 13. A wider counterbore may be provided toaccommodate a protection collar as explained subsequently. Next theimplant is inserted up to the first thread in the opening in the bone. Atool, such as a wrench, is used to engage the hex portion 12 and torotate the implant. The threads 13 are made to be self-tapping so thatthe implant portion will begin to screw down into the patient's bone. Ifnecessary, a bone tap can be used to create grooves in the hard uppercortical bone prior to insertion of the implant portion. The right anglesurface 18' of the channel also has self-tapping properties so as toease the insertion of the implant, once it has reached the depth of thechannels 18. Further turning of the implant causes the right anglesurface 18' to scrape off bone as the implant is being threaded and topush the resulting bone chips forward. This causes the bone chips tofall through the channels 18 and into the area of the vents 16 wherethey may penetrate into the interior cavity 14. To facilitate this, thechannels 18 are made wider towards the vents 16.

As a result of this structure, bone chips created during the implantprocedure tend to accumulate at the base of the implant in the patient'sbone. Because of the autogenous nature of these bone chips they promotethe growth of new bone in the area and speed the formation of new bonearound and through the implant such that it is anchored in place morerapidly.

In FIG. 5 there is shown an implant portion 10 which is nearly identicalto that shown in FIG. 1. The principal difference is that, rather thanhaving a hexagonal projection useful for applying torque to the implant,a hexagonal recess 12' is provided. In addition, the threaded aperture19' is made somewhat smaller and is located at the base of hexagonalrecess 12'. As explained previously, the threaded aperture 19' is usedfor attaching the implant portion of the device to the abutment portionOne embodiment of such an attachment is shown in FIG. 6.

In FIG. 6 the upper part of the implant portion 10 is shown partlybroken away and partly in section. It is shown partly broken away toexhibit the interior cavity 14 and the threads 13. Towards the upperpart of the implant portion it is shown in cross section. This implantportion is like that shown in FIG. 5 with a hexagonal recess 12' forrotating it into position in the bone. As shown in FIG. 6 the screw typeimplant portion 10 is connected to an abutment portion 20 that includesa transitional collar 21, an angled threaded shaft 24, and a toothsupport cylinder 31. The threaded shaft 24 has its lower end screwedinto threaded aperture 19' in the implant portion 10. The upper end ofthe threaded shaft, which is set at an angle to the lower end, isreceived within a threaded aperture 35 in tooth support cylinder 31.This cylinder 31 contains a recessed portion 32 which may be utilized infixing on to the cylinder via cement or some other convenient and wellknown method, a porcelain, plastic, or other dental tooth-coloredveneering material in the form of an artificial tooth.

The transitional collar 21 is located between the upper end of theimplant portion 10 and the cylinder 31. This collar has an angled uppersurface 25 and a perpendicular lower surface 23. The angle of the uppersurface is made to equal the angle of the upper part of the angled shaft24. While collar 21 surrounds threaded shaft 24, it does not engage itsthreads.

During an installation procedure the implant portion 10 is located inthe patient's bone as previously described. The gingival tissues canthen be replaced over the implant portion and several weeks or monthsallowed to pass while new bone grows around and through the implantportion. However, alternatively the artificial tooth can be connected tothe implant immediately. Whichever manner is chosen, the attachment isaccomplished by selecting an angled shaft and transition collar whichhave an angle which will cause the artificial tooth to be correctlyaligned with the other teeth of the patient. Therefore the dentist ororal surgeon must be provided with a variety of such shafts and collarswhich are at standard angles. Also during the insertion procedure thesurgeon must appropriately angle the opening in the bone so itpenetrates a reasonably thick area of good bone. This may require thatthe opening in the bone be drilled at an angle in order to avoidpenetrating a nearby sinus cavity, passing completely through the bone,or contacting a nerve bundle. However, in selecting the angle at whichthe implant is buried, care must be taken to make sure that this anglewill accommodate one of the standard angles available with the threadedshafts and collars, e.g. 10, 20 or 30 degrees, so as to result inalignment between the new artificial tooth and the remaining teeth ofthe patient.

Once the threaded shaft 24 is engaged with the implant portion 10, thecollar 21 is slipped over the free end of the shaft. Then the shaft isrotated so that it is firmly secured in the implant portion and isextending in the proper direction. With the collar in place over thisshaft, the cylinder portion 31 is threaded over the open or free end ofthe shaft until it makes tight contact with the upper surface of thecollar and begins to squeeze the collar between the cylinder and implantportions. Notches and recesses 22 and 27 are provided in the matingsurfaces such that, once the parts are screwed together, these notchesand recesses engage each other and prevent unintentional unscrewing ofthe portions of the implant. With this firm attachment completed, theartificial tooth can then be attached over the abutment cylinder 31.

In FIG. 6 the level the patient's bone is shown as dotted line 70. Sincethe implant portion is submerged in the bone, the line 70 intersects thelower portion of the transitional collar 20. The gum tissue line 72 istowards the upper portion of the transitional collar. As a result thecollar acts a barrier to prevent the encroachment of bacteria and foodinto the interior portion of the collar and the hex recess of theimplant portion.

With the embodiment of FIG. 6 fixed angles are provided to the dentistand he must work with the standard angles and the angle which he createsfor the bore in the patient's bone, in order to assure proper alignmentof the teeth. In some patients who have had serious bone disease, theamount of available good bone is limited and the dentist has only alimited amount of freedom in selecting the angle at which the bore forthe implant is made. Also with the embodiment of FIG. 6 it is necessaryfor a dentist to keep a stock of various angled shafts and collars. Thedifficultly presented by the type of implant in FIG. 6 is overcome bythe implant shown in FIG. 7.

In FIG. 7 the angled shaft and transition collar are replaced with aball and socket joint which allows for the setting of the angledrelationship between the implant portion and the abutment portion at anyselected angle within the range of motion of the ball and socket joint,e.g. up to 30-40 degrees. In FIG. 7 the threaded cavity 19 receives thethreaded shaft of a lower or inner abutment casing 42. This casing has agenerally Y-shape with the lower portion being the shaft that extendsinto and engage the threads of cavity 19. The upper portion of casing 42has a hemispherical surface 45 such that it can receive a ball 46. Anupper or outer casing 44 screws onto outer threads of the inner casing42 such that ball 46 is wrapped within the abutment casing, but is freeto rotate therein so as to create a ball and socket joint.

A relatively large set screw 48 penetrates the ball completely. This setscrew 48 has an internal threaded cavity 55 which passes through anupper hexagonal projection 56. Once the implant portion 10 has beenlocated in the bone at the optimal angle, the ball 46 is rotated suchthat the center axis of the set screw is at the proper angle formounting of an artificial tooth in line with other teeth in thepatient's mouth. Then the hexagonal portion 56 is rotated with a wrenchor other tool so the set screw comes into extreme frictional contactwith the hemispherical surface 45 of inner casing 42. This preventsfurther rotation of the ball and the set screw.

The artificial tooth structure in the embodiment of FIG. 7 has aninterior cylinder 50, about which the porcelain, plastic or other dentalmaterial is formed to create the artificial tooth structure. Thiscylinder 50 with the artificial tooth structure mounted thereon, isplaced on top of the hexagonal projection 56 and is then attachedthereto by means of a screw 52 which passes through the cylinder 50 andinto the threaded aperture 55 in set screw 48.

The bone line 70 is shown in FIG. 7 as being approximately mid-waythrough the lower abutment casing 42, while the gum line 72 is justbelow the upper edge of the outer or upper casing 44. Thus, the bonedoes not interfere with the setting of the proper angle for the abutmentand the tissue is not likely to contact moveable adjustment parts.

The arrangement of FIG. 8 is a modification of that shown in FIG. 7. Inthis arrangement the set screw 48, which has a threaded recess 55 at itsend in FIG. 7, is replaced with a set screw 49 that has a further screwthread 59 on the opposite side of the hex projection 56. This additionalscrew thread is used to mount an artificial tooth support cylinder 53which has an interior threaded cavity. However, this device isessentially located and fixed in position in the same manner as theimplant of FIG. 7. One difference with this implant of FIG. 8 is thatthe artificial tooth support cylinder 53 may extend down to and incontact with the outer casing 44. This is done above the gum tissue line72 as shown in the figure. Because of the contact between the cylinderand the casing 44, food and bacteria are prevented from entering betweenthese two parts and the likelihood of infection is reduced. However,this arrangement allows for somewhat less range of angular adjustment.In particular the arrangement of FIG. 7 is capable of an angularadjustment range of approximately 37 1/2°, while that of FIG. 8 islimited to about 30°.

As a further alternative, the set screw 48, rather than having aprojecting threaded portion located above the hexagonal adjustment nut56, may have a projecting cylinder which is internally threaded (notshown). Thus either a male or female connection of this type may be usedwithout difficulty.

In order to get increased angular adjustment, an arrangement such asthat shown in FIG. 9 may be used. The abutment arrangement of FIG. 9 isessentially the same as that of FIG. 7; however, the ball and socketjoint are made smaller and the ball sits higher in the socket joint.Further, the set screw 54 of FIG. 9 is made to have a beveled surface 57such that a greater angular rotation may be made before it contacts theupper part of the outer casing 44. With this arrangement nearly 45degrees of angular adjustment can be achieved.

The abutment cylinder 50 has a recess 51 to receive the outer end of theset screw 54. This allows for greater stability when it is attached tothe set screw by means of attachment screw 52. The cylinder 50 is alsoangled in the same manner as the surface 57 of the set screw 54 so thatit does not bind against the upper abutment casing 44 and limit angularrotation.

In FIG. 7-9 the ball rotates with the set screw during angularadjustment. However, as an alternative, the ball may remain stationeryand the abutment casing may rotate as shown in FIG. 10. In FIG. 10 athreaded ball joint 60 has a projecting threaded shaft 61 which isreceived in threaded recess 19 of the implant portion 10. Various sizeprotection washers or collars 65 can be located about the finial part67, which connects the ball to the threaded shaft, in order to cover theupper surface of whatever implant portion is used, thereby preventingbacteria and food from entering the bore. The opening in the bone can becountersunk as indicated by dotted line 70 so the collar can extend outbeyond the implant portion upper surface, and bone can grow over part ofthe upper surface of the collar.

A two-part casing 62, 64 is mounted on the ball 60. The casing includesouter casing portion 62, which secures the remote end of the ball, andan inner casing 64, which provides the main hemispherical surfaceagainst which the outer casing holds the ball in a rotatable manner.These two casing parts can be threaded together or attached to eachother in any convenient manner. Their attachment, however, is such thatthe casing may rotate freely on the ball.

At the opposite end of ball 60 from the screw threads is a hexagonalrecess 63, which is the means by which this threaded ball joint isscrewed into the threaded recess 19 of the implant portion. In thisarrangement the gum line 72 is shown about 1/3 up from the base of theball joint, but below the lower extension of casing 62.

A hexagonal projection 66 is provided on the inner casing 64. Thisprojection can be used to rotate the inner casing 64 so that the ball issqueezed between it and the outer casing 62 so that swiveling can beprevented when the arrangement is at the proper angle. A conventionalcylinder 50 for a dental prosthesis is attached to the inner casing 64by means of a screw 52. This screw 52 penetrates a threaded aperture inthe inner casing.

An enlarged view of the inner casing 64 is shown in FIG. 11A. The lowerperipherial extension 64, of this casing forms a wedge that projectsbetween the ball 60 and the outer casing 62 as shown in FIG. 10. Whenthe inner casing 64 is screwed down onto ball 60, the extension 64, actsto lock the abutment on the ball and prevents further rotation. In partthis locking is maintained due to the fact that the diameter of theextension 64' is slightly less that the distance across the ball at itslocation. As a result there is an outward flaring of the extension asshown by the arrows in FIG. 11A, which prevents the unthreading of innercasing 64.

Instead of a one piece casing as shown in FIG. 11A, the inner casing maybe in two parts as shown in FIG. 11B, where the extension 64' is part ofa locking ring or washer 64". With this arrangement the ball issurrounded by the ring 64" and the casing 64. As the casing is threadedinto contact with the ball it forces the ring to wedge between the ball60 and the outer casing to frictionally hold the ball. The outwardflaring of the extension at the end of this compression process tends toprevent the unthreading of the inner casing, which prevents the abutmentfrom becoming loose.

Installation of submergible implants is generally a two stage procedure.During the first stage the implant portion is buried in the bone and thetissue is restored in place over it. Time is allowed to pass while newbone grows about, and often over, the implant. The tissue is thenreopened at the start of the second stage. If bone has grown over thesubmerged implant, it must be removed by a burr before the abutment canbe installed. If the bone grows into the threaded aperture for theabutment, however, removal of this bone may be very difficult.Consequently, it is conventional to install a thread cap having a lowheight into the aperture during the first stage. However, bone alsogrows over this cap and it must be removed in order to replace the capwith the abutment. Removal of such bone may cause some loosening of theimplant portion.

With the present invention, the collar 65 is used with a screw 68 as atemporary cap as shown in FIG. 12. Even if bone grows up over the edgesof the collar 65, there is no need to remove it because it becomes partof the permanent abutment. In particular cover screw 68 is removedduring the second stage operation, which may require the removal of asmall amount of bone that has growth over the screw. Then the coverscrew 68 is replaced with threaded shaft of abutment ball 60 which hasthe abutment casings 62, 64 already installed. Thus the collar 65 whichis anchored in bone, need not be freed from the bone as in prior artcaps, but becomes part of the final abutment structure.

FIGS. 13 and 14 show front and side sectional views of an incisor of apatient which is supported by an implant according to the presentinvention. As can be seen, particularly from FIG. 14, the patient'supper front jaw bone has only a thin amount of good bone 11 and thisbone is at an angle to the regular alignment of the other incisors inthe patient's mouth. Utilizing the present invention, implant portion 10is located in the center of the main portion of this bone. After thisimplant portion 10 is firmly anchored in good bone, either immediatelyafter its insertion or after several weeks or months have been allowedto pass, the abutment portion is installed. The abutment portion is aball and socket joint like that in FIG. 7 having a set screw 48 whichlocks the ball 46 at the proper angle. The cylinder 50 of the artificialtooth support is then attached to the set screw via an attachment screw52. As shown in cross section in FIG. 14, cast metal 58 surroundscylinder 50 and a porcelain or plastic dental material 70 forms thetooth structure about the metal.

FIG. 15 illustrates a cross-sectional view of an abutment withshock-absorbing capabilities. This abutment may be adapted for use withany of the previously discussed implants and angular adjustment devices.

The abutment of FIG. 15 has a cylinder portion 70, upon which theartificial tooth is mounted. In addition it has a collar 72. Thecylinder and collar are connected by a screw 74. Screw 74 also acts toconnect the cylinder and collar 70,72 to the rest of the abutment inmuch the same way as screw 52 connects cylinder 50 to the rest of theimplants in FIGS. 7, 9 and 10.

A flexible buna rubber washer 76, such as that used for over dentures,is located between and separates the cylinder 70 and collar 72 so thatthe cylinder 70 may move with respect to the collar 72. Typically, theartificial tooth will be mounted only on the cylinder 70. As a result,some of the forces applied to the artificial tooth during chewing orbiting are absorbed by the flexible washer 76 and are not transmitted tothe collar 72 and the rest of the implant.

In order to make it easy to install the washer 76, the cylinder andcollar parts are formed such that they define an oval recess which seatsthe washer. The head 75 of the screw 74 and a peripheral flare 73 on thescrew tend to keep the washer within the oval recess.

During installation the washer is assembled between the cylinder 70 andcollar 72. Then the screw 74 is pushed down through the opening in thecylinder part. The flare 73 compresses the washer 76 slightly as itpasses through the washer. Then the screw 74 is passed through collar 72and threaded into the rest of the implant. At some point, the flare 73is drawn against the opening in collar 72. However, the threadingoperation is continued in order to wedge the flared part of screw 74into collar 72. This acts to keep screw 74 from unthreading after theartificial tooth is put into use.

FIG. 16 shows an alternative version of the screw 74 of FIG. 15. In thisalternative, the flared part 73 has a triangular cross-sectional shape.Once this screw has been pushed through the washer 76, it cannot bewithdrawn. Thus, it is necessary to cut the washer to remove it.

Besides being used to mount a single tooth, the implants according tothe present invention can be used as supports for a permanent bridge ora removable bridge. In the case of a removable bridge the abutmentcylinder is in the form of small copings which can be spaced throughoutthe edentulous span of a patient. These copings support a bar onto whichthe bridge structure may be screwed or clipped.

While the invention has been particularly shown and described withreference to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade thereon without departing from the spirit and scope of theinvention.

What is claimed is:
 1. An implant portion of an implant designed forsupporting a prosthetic structure comprising:an implant body havingthreads over at least part of its exterior surface and being adapted tobe threaded into an opening in a bone of a patient which bone has beenexposed by an incision in the covering tissue; and at least one channelformed such that it at least extends through threads on the body fordirecting bone chips toward a base portion of the opening in the bone,one edge of the threads at one side of the channel being substantiallyat a right angle to the circumferential direction of the threads, saidone edge being adapted (i) to promote self-tapping of the threads in thebone, (ii) to shave off pieces of bone during threading of the implantportion into the bone, and (iii) to direct the pieces of bone into thechannel such that the channel may direct pieces toward the base portionof the opening.
 2. An implant portion of an oral implant designed forsupporting an artificial tooth structure comprising:a generallycylindrical implant body having a plurality of circumferentialprojections extending over at least part of its exterior surface andbeing adapted to be installed in an opening in the bone of a patient byrotation thereof at least in part; and at least one channel formed suchthat it extends generally longitudinally through the projections of thebody for directing bone chips towards a base portion of the opening inthe bone, one edge of the projections at one side of said channel beingsubstantially at a right angle to the circumferential direction of theimplant body, said one edge being adapted (i) to promote self tapping ofthe projections in the bone during rotation of the body, (ii) to shaveoff pieces of bone during rotation of the implant body, and (iii) todirect the pieces of bone into the channel such that the channel maydirect the pieces toward the base portion of the opening.
 3. An implantas claimed in claim 2 wherein the projections are threaded and theimplant portion is installed by threading it into the opening in thebone.